1. Field of the Invention
The invention is directed to a network for compensating the non-linearity of an amplifier in accordance with the preamble of the main claim.
2. Description of the Prior Art
Cascade compensation networks of this type are known (DE-OS Nos. 2,140,851 and 2,306,294). Due to the auxiliary network, which is cascaded either before or behind the amplifier, the signal to be amplified is pre-distorted or, respectively, post-distorted as far as possible exactly inversely to the non-linear distortions of the amplifier, so that the distortions caused by the amplifier are compensated. FIG. 1 shows the basic circuit diagram for such a cascaded compensation network with the auxiliary network A disposed before the amplifier B. The amplifier B has a frequency-dependent non-linear transfer function with a linear component H.sub.1b (.omega.), a quadratic component H.sub.2b (.omega..sub.1, .omega..sub.2) and a cubic component H.sub.3b (.omega..sub.1, .omega..sub.2, .omega..sub.3). The auxiliary network is composed, for instance, of three branches 1, 2, 3 which are connected in parallel between a branch point 4 and an adder 5. Mostly, branch 1 connects the branch point 4 directly to the adder 5; for compensation of the quadratic distortions a circuit component H.sub.2a is arranged in branch 2 by which the input signal X is distorted quadratically and is inversely supplied to the adder 5. For compensating cubic distortions, a corresponding circuit component H.sub.3a may be arranged in the branch 3 for cubically distorting the input signal X and again supplying it inversely to the adder 5. With the known auxiliary networks the circuit components H.sub.2a and H.sub.3a are components such as diode or resistance networks the transfer functions of which approximately correspond at only one frequency to the corresponding quadratic or cubic characteristic of the amplifier B at the same frequency; moreover, in the known networks additional phase shifters are frequently provided in the branches 2 and 3 by means of which the desired matching of the characteristics between the auxiliary network A and the amplifier B can be adjusted exactly for only one selected frequency. Therefore the known auxiliary networks are only narrow-band solutions, while broadband compensation of the non-linearities of such an amplifier within a broad transmission frequency band is not possible with the known auxiliary networks.